Plate-type heat exchanger devices are well known in the art.
These devices are constituted by a fixed and a movable endplate, one or both being provided, according to different applications, with inlet and outlet connections for fluids, a pack of metallic plates, generally stainless steel plates, being disposed between said endplates.
Said metallic plates, which are bored close to their angled edges in order to allow the circulation of the fluids, constitute the surface of thermal exchange between the fluids and are provided with a series of ribs suitable to increase the exchange surface and the fluid turbulence in order to obtain relevant thermal exchanges.
Generally, said ribs are disposed according to a herringbone or a so-called laundress-board pattern.
Furthermore, the periphery of such plates is provided with sealing gaskets made of an elastic, rubber-like material, which delimit and physically separate the pair of channels formed inside of the heat exchanger and within which the fluids flow.
This type of device is generally used in applications of various kinds, e.g. for instantaneously producing sanitary hot water by means of a boiler, with or without buffers, or for the heating exploiting geothermal gradients, or for swimming-pool heating by means of a boiler, or for a district-heating network.
Obviously, in accordance with particular applications, said devices are differently dimensioned in what concerns the surface and the number of plates, as well as the different feeding circuits, in series or in parallel, to be used to convey the fluids to the plates.
As regards to the sealing gaskets, which are placed peripherally to said plates, they play a determinant role in the operation of plate-type heat exchangers.
In fact, said gaskets have to be made of high quality materials allowing the gaskets to carry out a perfect seal at high temperatures and pressures, as well as to hold their efficiency even after thousands of hours of operation.
Furthermore, they should perfectly match to suitable grooves the plates of heat exchangers are provided with, said grooves, on their turn, allowing the gaskets to be placed against possibly vertical walls in order to obtain a good support against the thrust which is exerted on the gasket from the inner side of the exchanger and this, particularly, in proximity of the fluid inlet bores.
The background art proposes different solutions in order to allow the gaskets to be correctly placed inside of the grooves present in the plates of plate-type heat exchangers.
A first known solution provides for the use of a suitable glue in order to stick the gasket on the groove's bottom.
However, this solution involves a plurality of disadvantages and drawbacks which are due to the complex maintenance of the plates and/or to the complex replacement of the gaskets, as well as very high material and labour costs.
In fact, a sticked gasket should be replaced by eliminating the old bonding agent by means of a suitable solvent; this operation should be carried out with care, in order to avoid damaging of the plate.
Thereafter, the groove should be carefully cleaned, and a new glue layer is placed in the same; then, a new gasket is placed into the groove and it is necessary to wait till it perfectly adheres to its seat.
Of course, this involves remarkable loss of time due to the carrying out of all the above cited operations and, in particular, of the sticking operation.
In the field of bolding agents, Italian Patent n. 1.257.033 discloses the use of an acrylic adhesive layer the chemical-physical features of which are suitable for fixing the sealing gaskets to the plates of plate-type heat exchangers.
In fact, since said acrylic adhesive is particularly sensitive to pressure and is also provided with high setting velocity, it allows the gasket to be immediately placed on the plate, just after the acrylic adhesive has been spread.
Furthermore, the acrylic adhesive according to said technical solution allows the coupled elements to be removed and connected again, without decreasing the glueing activity and without leaving adhesive traces on the gasket and on the plate allowing the easy replacement of the gasket if necessary.
Another solution well known to the skilled man is disclosed in European Patent Application EP-A-0 039 229, where no mention is made of bonding agents.
According to said document the periphery of the gasket is provided with a series of substantially cylindrical protuberances which are suitable for being housed, by exerting a pressure on them, into corresponding holes which are present along the external periphery of said plate.
However, this solution involves drawbacks too, since it requires, for example, a very high precision for positioning the gasket relative to the plate in such a way as each protuberance is aligned to the corresponding plate hole.
Furthermore, it is apparent that such a technical solution requires specific plates provided with suitables holes for the connection of the gasket to the plate; thus, said modified plates can not be universally used.
Document WO 85/00052 shows a further technical solution for coupling a sealing gasket to a plate of a plate-type heat exchanger.
According to said document, the sealing gasket is provided with a series of tabs which are made of the same rubber material as the gasket and which are formed on the external periphery of the gasket.
In operation, these tabs are inserted into cavities which are formed between the upper and lower surfaces of the plate, and they allow a sufficiently quick positioning of the gasket into the groove.
However, this solution involves drawbacks too, since the gasket is positioned in a rather rough way relative to the groove.
Furthermore, since the fastening tabs are necessarily made of rubber, they cannot show a high strength against thermal and mechanical stresses which a gasket normally undergoes during its working life.
As a result, the gasket gets frequently out of the groove, thereby causing leakages in the heat exchanger.